Principal Components – Based Techniques in Voltammetric Determination of Caffeic,Syringic and Vanillic Acids

It was demonstrated that Principal Components Analysis and Principal Components Regression support qualitative and quantitative investigation of three‐component synthetic samples containing micromolar concentration of caffeic acid (CA), syringic acid (SA) and vanillic acid (VA), in various proportions. The first, second and third PCs enable modelling of relationships and distinction of objects of different composition. Optimized and validated multivariate calibration models, implemented on the basis of the samples selected with the help of 3‐level full factorial design, effectively support simultaneous determination of the considered analytes. Obtained RMSEP was no higher than 0.23 μm for CA, 0.17 μm for SA and 0.21 μm for VA, in relation to the concentration of 1.9 to 21.4 μm of each compound. Recovery between 90–108% for considered analytes, determined in synthetic wine solution, was additional verification of calibration model. Application of automatic baseline correction was extensively studied.     

Photooxygenation of 3-aryl-2-cyclohexenols: synthesis of a new series of antimalarial 1,2,4-trioxanes

Using easily accessible 3-aryl-2-cyclohexenols, a photooxygenation route for the preparation of bicyclic 1,2,4-trioxanes is reported. Several of these trioxanes have shown significant antimalarial activity against multidrug resistant Plasmodium yoelii in mice by the oral route.     

Development and validation of a generic liquid chromatographic method for the simultaneous determination of five commonly used antimalarial drugs: Application to pharmaceutical formulations and human plasma

A simple, sensitive, and rapid liquid chromatographic method was developed and validated using diode array detection for the determination of five commonly used antimalarial drugs in pharmaceutical formulations and in human plasma. Chromatographic separation of antimalarial drugs and internal standard (ibuprofen) was achieved on a C₁₈ column with a mobile phase composed of 10 mM dipotassium orthophosphate at pH 3.0, methanol, and acetonitrile in a ratio of 20:38:42 v/v, at a flow rate of 1 mL/min. The analytes were monitored at 220 nm and separated in ?10 min. The method was validated for linearity, accuracy, precision, limit of quantification, and robustness. Both intra‐ and interday precisions (in terms of %RSD) were lower than 3% and accuracy ranged from 98.1 to 104.5%. Extraction recoveries were ≥96% in plasma. The limits of quantitation for artemether, lumefantrine, pyrimethamine, sulfadoxine, and mefloquine were 0.3, 0.03, 0.06, 0.15, and 0.15 μg/mL in human plasma. Stability under various conditions was also investigated. The method was successfully applied for quantification of antimalarial drugs in marketed formulations and in spiked human plasma. The method can be employed for routine QC purposes and in pharmacokinetic investigations.     

Innovative high-performance liquid chromatography method development for the screening of 19 antimalarial drugs based on a generic approach, using design of experiments, independent component analysis and design space

An innovative methodology based on design of experiments (DoE), independent component analysis (ICA) and design space (DS) was developed in previous works and was tested out with a mixture of 19 antimalarial drugs. This global LC method development methodology (i.e. DoE-ICA-DS) was used to optimize the separation of 19 antimalarial drugs to obtain a screening method. DoE-ICA-DS methodology is fully compliant with the current trend of quality by design. DoE was used to define the set of experiments to model the retention times at the beginning, the apex and the end of each peak. Furthermore, ICA was used to numerically separate coeluting peaks and estimate their unbiased retention times. Gradient time, temperature and pH were selected as the factors of a full factorial design. These retention times were modelled by stepwise multiple linear regressions. A recently introduced critical quality attribute, namely the separation criterion (S), was also used to assess the quality of separations rather than using the resolution. Furthermore, the resulting mathematical models were also studied from a chromatographic point of view to understand and investigate the chromatographic behaviour of each compound. Good adequacies were found between the mathematical models and the expected chromatographic behaviours predicted by chromatographic theory. Finally, focusing at quality risk management, the DS was computed as the multidimensional subspace where the probability for the separation criterion to lie in acceptance limits was higher than a defined quality level. The DS was computed propagating the prediction error from the modelled responses to the quality criterion using Monte Carlo simulations. DoE-ICA-DS allowed encountering optimal operating conditions to obtain a robust screening method for the 19 considered antimalarial drugs in the framework of the fight against counterfeit medicines. Moreover and only on the basis of the same data set, a dedicated method for the determination of three antimalarial compounds in a pharmaceutical formulation was optimized to demonstrate both the efficiency and flexibility of the methodology proposed in the present study.     

Selective Determination of Verapamil in Pharmaceutics and Urine Using a Boron‐doped Diamond Electrode Coupled to Flow Injection Analysis with Multiple‐pulse Amperometric Detection

This work presents a simple and low‐cost method for fast and selective determination of Verapamil (VP) in tablets and human urine samples using a boron‐doped diamond working electrode (BDD) coupled to a flow injection analysis system with multiple pulse amperometric detection (FIA‐MPA). The electrochemical behaviour of VP in 0.1 mol L⁻¹ sulfuric acid showed three merged oxidation peaks at around +1.4 V and upon reverse scan, one reduction peak at 0.0 V (vs. Ag/AgCl). The MPA detection was performed applying a sequence of three potential pulses on BDD electrode: (1) at +1.6 V for VP oxidation, (2) at +0.2 V for reduction of the oxidized product and (3) at +0.1 V for cleaning of the working electrode surface. The FIA system was optimized with injection volume of 150 μL and flow rate of 3.5 mL min⁻¹. The method showed a linear range from 0.8 to 40.0 μmol L⁻¹ (R>0.99) with a low limit of detection of 0.16 μmol L⁻¹, good repeatability (RSD<2.2 %; n=10) and sample throughput (45 h⁻¹). Selective determination of VP in urine was performed at+0.2 V due to absence of interference from ascorbic and uric acids in this potential. The addition‐recovery tests in both samples were close to 100 % and the results were similar to an official method.     

Quantitative structure activity relationship (QSAR) studies on a series of imidazole derivatives as novel ORL1 receptor antagonists

QSAR studies were performed on a series of imidazole derivatives as novel Orl1 receptor antagonists. Imidazole derivatives have been analyzed in relation to their physicochemical and molecular properties. The activities of the compounds were found to be significantly correlated with the physicochemical parameters such as density (D), surface tension (St), index of refraction (Ior), balaban index (J) and partition coefficient (Log P). It was found that the presence of group at R₁ position was conducive for the inhibitory activity. The results are critically discussed on the basis of regression data and cross validation techniques. Poglani factor Q and the results of LOO (leave one out) method confirms the reliability and predictability of the proposed models.